Today, the production of bio-fuels, as an alternate or a substitute to gasoline is deemed as a potential strategy to contend with the rising demands of oil for energy. United States alone consumes about 25% of the total world's production of oil while it has less than 3% of the world's oil reserve. The recent expansion of the bio-fuels industry has fueled the popularity and increased awareness of the effects of ethanol on the environment, economy and US national policy. Antimicrobials have been used in fermentation during the production of fuel alcohol since its inception dating back to the 1970's. The co-products (distillers grains) resulting from these fermentations have been fed to livestock increasingly over the past 3 decades with a particularly sharp increase of 340% from 1999 to 2005 to 8.35 million metric tons of distillers grains in the United States alone. Most (98%) of the distillers grains in North America come from plants that produce ethanol for oxygenated fuels.
Alcohol is produced by yeast fermentation, of carbohydrates primarily derived from starch-based or sugar-based feedstocks. This fermentation is provided by yeast, specifically the microorganism Saccharomyces cerevisiae that ferments the available carbohydrates to produce ethanol. The entire process of alcohol production is well documented in “The Alcohol Text Book”, 4th edition, Jacques, Lyons & Kelsall, published by Nottingham University Press, 2003, which is incorporated herein by reference.
One of the important concerns with a conventional fermentation system is the difficulty of maintaining a clean, disinfected and sterile condition which is free from contaminating bacteria in the large-sized batches during the long fermentation period. Unfortunately, the optimum environment for fermentation is also extremely conducive to bacterial growth. If a batch becomes contaminated, not only must the fermentation mixture (i.e. the yeast, feedstock, nutrients, water, etc.) be discarded, but the entire fermentation vessel must be emptied, cleaned, disinfected or sterilized as per the protocol of a production facility. This process adds unwanted costs and loss of production.
It is common in current commercial fermentation processes for contaminating bacteria to infect the fermentations and consume the available carbohydrate consequently causing less carbohydrate availability to the preferred yeast fermentation. Contamination by bacteria is very costly to the ethanol producer and a variety of control methods are utilized to limit this event. It is commonplace in most ethanol producing facilities to utilize caustic washing via clean in place systems.
The origin of these contaminants is multi-faceted and is being studied and contemplated by both researchers and producers. It is generally accepted that much of the bacteria originates from the incoming feedstock since the starch crops are often contaminated with bacteria from the field and storage silos. Jet cooking the fermentation substrate (mash) helps lower the bacteria count, but does not completely eliminate the contaminants as this process is not a sterilization procedure. Bacterial contamination is unavoidable because these production facilities are not sterile environments like those commonly found in the pharmaceutical industry.
With the increased popularity of the bio-fuels industry, alcohol productions along with distillers co-products have increased steadily over the years. This has caused heightened awareness and concerns regarding the use of antimicrobials during the fermentation process and the possibility that antimicrobials “carry through” to the resulting distillers co-products.
The industry is currently awaiting more direct guidance from the Food & Drug Administration (FDA) and the Center for Veterinary Medicine (CVM) as well as certain state agencies (where applicable) on the allowable use of antimicrobials as a processing aid in ethanol production.
An economical method to selectively control contaminating bacteria is needed. The method must utilize smaller amounts of an antibiotic or a combination of antibiotics than currently being used to target and act as bactericidal and/or bacteristatic to control contaminating bacteria in fermentation, such as a bacterial contaminant found in the production of fuel alcohols, beverage alcohols and industrial alcohols while improving production yield. Additionally, distillers co-products from the fermentation must be safe for direct feeding to animals, i.e., the antibiotic used must not be detectable in the distillers co-products in order to comply with increasing state and federal regulation. From the alcohol producer's point of view, the antibiotic needs to be cost effective and would be of more value if it did not have a deleterious effect on the yeast, thus producing more alcohol. Further, the antibiotic needs to be less susceptible to resistance by the targeted bacteria and be effective in low concentrations while not carrying through to the distillers grams.